1. Technical Field
The present invention relates to a high-speed imaging apparatus such as a video camera which is capable of slow-motion playback.
2. Background Art
In recent years, video cameras have been increasingly having higher performance and particularly have been enabled to perform slow-motion shooting for capturing images at speeds higher than normal speeds along with the development of digital technologies. Particularly, in cases of broadcasting sports program, beautiful slow-motion playback pictures are a significant strong point in program production.
For capturing images at higher speeds, there is a need for providing signals having a frequency range corresponding to multiples of the speed of conventional standard video signals. Namely, for capturing images at a treble speed in order to perform ⅓-slow playback, there is a need for a treble frame rate in outputting from a camera, thereby requiring a data rate which is three times a normal data rate. Namely, the camera is required to output data in a different format from those of normal video signals at a treble speed, and there is also a need for a transfer device dedicated to high-speed imaging in order to transfer such signals.
As a method for overcoming the problem, Japanese Patent Laid-open Publication No. 11-32241 (pages 3 to 5) discloses a camera apparatus, for example. FIG. 20 is a block diagram illustrating the structure of the camera apparatus. In the camera apparatus, a CCD imaging unit 101 employs a CCD (Charge Coupled Device) image sensors as a solid-state imaging element which performs photoelectric conversion. In the CCD imaging unit 101, a transfer unit 102 transfers charges at a driving speed fc, and imaging output signals therefrom are subjected to A/D conversion and then are accumulated in a field memory 103.
In the case of capturing images at a treble speed by the camera apparatus, namely in the case of n=3, the transfer unit 102 drives the CCD imaging unit 101 at a driving speed 3 fc which is three times a normal driving speed, and output signals therefrom are subjected to A/D conversion at a sampling frequency 3 fc which is three times a normal sampling frequency. The imaging signals having the treble speed are stored at #1 to #3 in the field memory 103. Further, the imaging unit 101, the transfer unit 102 and the field memory 103 operate on receiving control signals from a control circuit 105.
While the image signals are written into the field memory 103 at the clock frequency 3 fc, the contents of the field memory are read out therefrom at a normal clock frequency fc in parallel thereto, then are attenuated to ⅓ by 1/n attenuators 106 and are transferred to an adder 107. Accordingly, the adder 107 outputs the average value of the contents of #1 to #3 in the field memory 3 at a normal speed.
During capturing images at a normal speed, the contact point in a signal switcher (selector) 108 comes into contact with a side a, so that signals are directly extracted from the transfer unit 102 in the CCD and transferred to a camera signal processing circuit 109. On the other hand, during high-speed imaging and during low-speed photographing, the contact point comes into contact with a side b, so that outputs from the adder 107 are transferred to the camera signal processing circuit 109. The signals which have been processed by the camera signal processing circuit 109 are transferred to subsequent circuits which perform recording and monitoring thereof according to well-known methods.
Further, in order to enable playbacking signals created by photographing at a high-speed later at a normal speed, the image signals are written into a buffer memory 104 at a higher speed. Subsequently, the photographing is stopped or image signals which have been stored in the buffer memory 104 at this time are read out therefrom at the normal speed, instead of signals being created by photographing.